feat(安全): 添加安全开关并完善测试流程

实现安全开关默认关闭与响应头透传逻辑
- URL 校验与响应头过滤支持开关并覆盖流式路径
- 非流式 Content-Type 透传/默认值按配置生效
- 接入 go test、golangci-lint 与前端 lint/typecheck
- 补充相关测试与配置/文档说明

backend/internal/util/responseheaders/responseheaders_test.go

@@ -0,0 +1,67 @@
+package responseheaders
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+)
+
+func TestFilterHeadersDisabledPassThrough(t *testing.T) {
+	src := http.Header{}
+	src.Add("Content-Type", "application/json")
+	src.Add("X-Test", "ok")
+	src.Add("X-Remove", "keep")
+	src.Add("Connection", "keep-alive")
+	src.Add("Content-Length", "123")
+
+	cfg := config.ResponseHeaderConfig{
+		Enabled:     false,
+		ForceRemove: []string{"x-test"},
+	}
+
+	filtered := FilterHeaders(src, cfg)
+	if filtered.Get("Content-Type") != "application/json" {
+		t.Fatalf("expected Content-Type passthrough, got %q", filtered.Get("Content-Type"))
+	}
+	if filtered.Get("X-Test") != "ok" {
+		t.Fatalf("expected X-Test passthrough, got %q", filtered.Get("X-Test"))
+	}
+	if filtered.Get("X-Remove") != "keep" {
+		t.Fatalf("expected X-Remove passthrough, got %q", filtered.Get("X-Remove"))
+	}
+	if filtered.Get("Connection") != "" {
+		t.Fatalf("expected Connection to be removed, got %q", filtered.Get("Connection"))
+	}
+	if filtered.Get("Content-Length") != "" {
+		t.Fatalf("expected Content-Length to be removed, got %q", filtered.Get("Content-Length"))
+	}
+}
+
+func TestFilterHeadersEnabledUsesAllowlist(t *testing.T) {
+	src := http.Header{}
+	src.Add("Content-Type", "application/json")
+	src.Add("X-Extra", "ok")
+	src.Add("X-Remove", "nope")
+	src.Add("X-Blocked", "nope")
+
+	cfg := config.ResponseHeaderConfig{
+		Enabled:           true,
+		AdditionalAllowed: []string{"x-extra"},
+		ForceRemove:       []string{"x-remove"},
+	}
+
+	filtered := FilterHeaders(src, cfg)
+	if filtered.Get("Content-Type") != "application/json" {
+		t.Fatalf("expected Content-Type allowed, got %q", filtered.Get("Content-Type"))
+	}
+	if filtered.Get("X-Extra") != "ok" {
+		t.Fatalf("expected X-Extra allowed, got %q", filtered.Get("X-Extra"))
+	}
+	if filtered.Get("X-Remove") != "" {
+		t.Fatalf("expected X-Remove removed, got %q", filtered.Get("X-Remove"))
+	}
+	if filtered.Get("X-Blocked") != "" {
+		t.Fatalf("expected X-Blocked removed, got %q", filtered.Get("X-Blocked"))
+	}
+}